What I think is this.
(A) is essentially fully explained by (1). It may be that (3) also had a role, but there is at the moment basically no evidence for this. If the more left-wing, Miliband message had produced a result like this in 2020, then there'd be more reason to go for (3). But a result in which Labour makes modest net gains on the Tories in England, but not enough to seriously threaten their government, is more or less what you'd expect in a poll where a first-term government stands for reelection with the economy in reasonable shape.

(B) is not explained by (1), but is fully explained by (2). Undo the Scottish wipeout and Labour's result, as I said yesterday, is not a disaster at all and wouldn't have prompted this degree of soul-searching and calls for internal reform.

It is true that, looking to the 2020 election, Labour needs to improve its showing in England and Wales. But it actually did improve its showing in England and Wales at this election, by about as much as you could reasonably expect. Maybe this is the limit for a programme further left than New Labour, and the party really does need to return to that aspirational centre to do any better. And you can understand why people who already believed New Labour is the best programme, like Chuka Umunna and Tony Blair and Peter Mandelson, are seizing the opportunity to make this claim. But presently there is very limited evidence that Ed Miliband's more left-leaning programme is doomed to failure.